Field of the Invention
The present disclosure relates generally to centrifugal compressors, and more particularly, to droplet catchers for removal of liquid from the compressor environment. This disclosure also relates to centrifugal compressors comprising such devices, and methods of improving the performance of the compressors with the devices.
Description of the Prior Art
A compressor is typically used to boost pressure of a working fluid by receiving power from an electric machine or a turbine, and applying a compressive force to the working fluid. The working fluid may be air, gas, refrigerant, or the like. Compressors are typically classified as positive displacement compressors, dynamic compressors, or turbo compressors, depending on the method they employ for compression.
Positive displacement compressors are typically used to boost pressure of the working fluid by reduction in volume. One type of positive displacement compressor is a centrifugal compressor. Centrifugal compressors operate by accelerating the working fluid (e.g., gas) through the use of rotating blades, and then restricting the exiting gas so that it is compressed.
Contaminants, such as liquid or solid particles, in the inlet gas can have a severe effect on compressor reliability. Mechanical failures of centrifugal compressors can be caused in many instances by liquid aerosol contamination (i.e., liquid droplets) of the intake gas. Liquid droplets may accumulate in a stream of gas by condensation as the gas impacts surfaces within the compressor. FIG. 1 illustrates a portion of a prior art centrifugal compressor and the gas-liquid droplet flow pattern seen in such current centrifugal compressors. As FIG. 1 shows, droplets first impact the compressor at the surface of the impeller 14, particularly the blades 16 of the impeller.
The droplets 12 hit the rotating impeller 14, collide with each other, and form larger droplets. While a portion of the larger droplet is likely to continue on in the gas flow direction of the compressor, the remaining portion of the larger droplet sticks to the rotating impeller surface. This larger droplet is now more likely to coalesce with new droplets impacting the surface. The droplets thus become larger, their evaporation is hindered, and their erosive potential is higher. The liquid phase volume in the compressor can increase and the efficiency of the compressor is reduced proportionally. The liquid film that forms on the blade surface or casing due to droplet deposition can become unstable and can also lead to formation of droplets of large size that are potentially very harmful as far from an erosion standpoint. Over time, the increased liquid phase volume and contaminants associated therewith will corrode and damage the compressor, leading to failure, or at least frequent shut downs for inspection and repair.
Whenever a non-negligible amount of water is contained in the stream at the inlet, droplet separation devices are installed upstream of the first stage in current centrifugal compressors to separate all the water content from the mixture. Current droplet separation devices, however, provide no separation technique that captures the liquid droplets before they are able to coalesce and become larger. This results in a strong intercooling effect, delayed evaporation and a high local volume faction/concentration of the liquid phase, thereby strongly affecting the performance of the compressor.